caddyfile: Error on invalid site addresses containing comma (#4302)
caddyfile: Error on invalid site addresses containing comma (#4302)

Some users forget to use a comma between their site addresses. This is invalid (commas aren't a valid character in domains) and later parts of the code like certificate automation will try to use this otherwise, which doesn't make sense. Best to error as early as possible.

Example thread on the forums where this happened: https://caddy.community/t/simplify-caddyfile/13281/9
l3dlp/caddy,l3dlp/caddy,mholt/caddy,mholt/caddy,l3dlp/caddy